The present invention relates to an inkjet printer for recording an image onto a recording medium by emission of ink particles to this recording medium.
An image recording method using an inkjet printer is often used as an image recording method for handy and economical image recording. A serial type inkjet printer feeds recording media of paper intermittently in the sub-scanning direction, and, when the recording media are stopped, moves the head on the recording media in the main scanning direction perpendicular to the sub-scanning direction. While the head is moving in the main scanning direction, the inkjet printer emits ink particles onto the recording media from the head by means of a piezoelectric element or a heater. An image is recorded on the recording medium by the operation of such an inkjet printer.
Ink used in an inkjet printer includes the active ray cure ink that is cured by application of active ray including ultraviolet ray and electron beam. The active ray cure ink is composed, for example, of color material, polymerizable monomer or oligomer, photopolymerization initiator for promoting monomer and oligomer crosslinking reaction and polymerization reaction by photocatalystic reaction, and photopolymerization accelerating agent. This ink is cured by crosslinking reaction or polymerization reaction by irradiation of active ray. The printer using such active ray cure ink for recording is less foul smelling than the printer using solvent based ink for recording, and is capable of recording on a recording medium having no ink absorbing ability. For these features, this ink has been drawing attention in recent years.
As disclosed in the Patent References 1 and 2, the inkjet printer for recording with ultraviolet cure ink cured by ultraviolet ray is provided with a UV source emitting ultraviolet rays. This printer emits ink particles of ultraviolet cure ink from the head to the recording medium, and moves the recording medium or head, whereby ultraviolet ray is applied to the ink particles landed on the recording medium from the UV source. This allows ink particles landed on the recording medium to be cured.
[Patent Reference 1]
Official Gazette of Japanese Application Patent Laid-Open Publication No. 2002-11860 (FIG. 19, pages 10 and 11)
[Patent Reference 2]
Official Gazette of Japanese Application Patent Laid-Open Publication No. S60-132767
If a long time is required between hitting of ink particles and the exposition to ultraviolet, the landed ink particles are not cured, and cause spread of the ink on the recording medium. To ensure a high quality print image, it is preferred that ink particles be exposed to ultraviolet rays immediately subsequent to the ultraviolet cure ink landing the recording medium, thereby allowing the ink particles to be cured. To do so, the head is placed close to the UV source so that ultraviolet rays are launched into ink particles immediately after they have hit the medium. However, the UV source emits ultraviolet rays radically. So if the head comes too close to the UV source, ink particles are exposed to ultraviolet rays before hitting the medium, and are cured, with the result that recording failure occurs. If the head comes too close to the UV source, ultraviolet rays emitted from the UV source will irradiate the head. If they have irradiated the head, ultraviolet cure ink present at the head outlet may be thickened or cured, and may not come out of the outlet.
To solve this problem, the object of the present invention is to provide a means for ensuring ink particles to be cured immediately after hitting a recording medium without allowing it to be cured before hitting.
The above object can be attained by the following configurations.
In the first configuration, an inkjet printer comprises: a head for emitting to a recording medium the ink to be cured by exposure to active ray, an active ray source for emitting active ray wherein the aforementioned active ray source is arranged backward in the direction of the relative movement of the head toward the recording medium during emission of ink, and on the side where the head is arranged with respect to the aforementioned recording medium, and a shielding member that prevents the active ray from the active ray source from directly or indirectly entering into the trajectory formed by ink particles emitted from the head and reaching the recording medium.
The invention of the first configuration uses a shielding member that prevents the active ray emitted from the active ray source from entering directly or indirectly the trajectory formed by ink particles emitted from the head and reaching the recording medium. This function decreases the possibility that ink particles emitted from the head are exposed to active ray before hitting the recording medium and are cured, and ensures the recording with high image quality. Use of such a shielding member permits the active ray source to be installed closer to the head. Thus this makes it possible that, immediately after hitting the recording medium, ink particles are exposed to the active ray coming from the active ray source, and are hence cured immediately after hitting the recording medium without ink particles unnecessarily spreading on the recording medium or blotting.
Since the shielding member prevents the active ray emitted from the active ray source from entering into the starting point of an ink particle trajectory, namely the ink outlet of the head, the ink at the outlet of the head is restrained from being thickened or cured. This function prevents the ink outlet from being clogged for a long period.
Here, direct entry of the active ray into the ink particle trajectory is defined as entry of the active ray from the active ray source into the ink particle trajectory without being reflected by inkjet printer parts or recording medium. Indirect entry of active ray into the ink particle trajectory is defined as entry of the active ray from the active ray source into the ink particle trajectory after having been reflected at least once by inkjet printer parts or recording medium.
In the second configuration, an inkjet printer according to the first configuration is further characterized in that the aforementioned shielding member is arranged between the aforementioned active ray source and head, and is provided with a first extension member extending toward the recording medium further than the surface of the head where ink particles are emitted.
According to the invention having the second configuration, the first extension member extends toward the recording medium further than the ink-emitting surface of the head between the active ray source and head. The active ray emitting from the active ray source is further shielded by the first extension member, and hence it becomes possible to prevent the active light from reaching the trajectory of ink particles. Accordingly, ink particles emitted from the head are not cured before hitting the recording medium. This allows the active ray source to be installed closer to the head. Thus, it becomes possible that ink particles are cured immediately after hitting the recording medium so that a high quality image is recorded on the recording medium.
In a third configuration, an inkjet printer according to the second configuration is further characterized in that the aforementioned shielding member is provided with a second extension member extending from the first extension member toward the trajectory in the direction crossing the direction in which the first extension member extends.
The invention of the third configuration has a second extension member which extends from the first extension member toward the ink particle trajectory (namely, in the crossing direction of the trajectory). Accordingly, the active ray reflected by the recording medium is cut off by the second extension member so that the active ray is hardly launched on the surface of the head where ink particles are emitted. This allows the active ray source to be installed closer to the head, with the result that ink particles can be cured immediately after having hit the recording medium.
In the fourth configuration, an inkjet printer according to the first configuration is further characterized in that the surface of the aforementioned second extension member opposite to the recording medium is designed in a rugged (convexo-concavo) form.
According to the invention having the fourth configuration, the surface of the second extension member opposite to the recording medium is designed in a rugged form. This can make possible to reduce the active ray being reflected by the second extension member at the surface area opposite to the recording medium, even when the active ray emitted from the active ray source enters at the second extension member, by the effects of scattering at the rugged surface and/or inner reflection at the second extension member. So even if active ray is repeatedly reflected between the second extension members and recording medium, it becomes possible to further prevent the active ray from entering into the ink particle emitting surface of the head or the trajectory. This configuration allows the active ray source to be installed closer to the head, with the result that ink particles can be cured immediately after hitting the recording medium.
In the fifth configuration, the inkjet printer according to the third and fourth configurations is further characterized in that the surface of the second extension member opposite to the recording medium absorbs active ray.
In the invention having the fifth configuration, the surface of the second extension member opposite to the recording medium absorbs active ray, even when the active ray is emitted from the active ray source and reflected by the recording medium to enter the area of second extension member. According to this feature, it becomes possible to prevent the active ray from being repeatedly reflected between the second extension member and recording medium, and from entering the ink particle emitting surface of the head or the trajectory. This configuration allows the active ray source to be installed closer to the head, with the result that ink particles can be cured immediately after hitting the recording medium.
In the sixth configuration, the inkjet printer according to any one of the first through fifth configurations is further characterized in that the aforementioned head, active ray source and shielding member are mounted so that they can move integrally with one another in the aforementioned direction of the relative movement.
According to the invention having the sixth configuration, the head is mounted movably in the direction of relative movement. This arrangement provides an inkjet printer where the image recording system is based on a serial method. Further, the active ray source is designed integrally movable with the head. Because of this arrangement, ink particles hitting the recording medium out of the head are exposed to the active ray source by the movement of the head and active ray source. Further, since the shielding member is mounted movable integrally with the head and active ray source in the direction of relative movement, an inkjet printer of serial method having the same effects as that of any one of configuration described in configuration 1 to 5 can be provided with simple structure and with simple mechanism.
In the seventh configuration, the inkjet printer according to any one of the first through fifth configurations is further characterized in that the aforementioned recording medium is fed in the reverse direction of relative movement, and the head is arranged along the direction orthogonal to the above-mentioned direction of relative movement.
According to the invention in the seventh configuration, the head is mounted along the direction orthogonal to the direction of relative movement. This arrangement provides an inkjet printer where the image recording system is based on a line head method. Since the active ray source is arranged backward the head in the direction of relative movement of the head in respect to the recording medium, ink particles having hit the recording medium out of the head are exposed to the active ray source as the recording medium is transported. And inkjet printer of line head method having the same effects as that of any one of configuration described in configuration 1 to 5 can be provided with simple structure and with simple mechanism.
In the eighth configuration, the inkjet printer according to any one of the first through seventh configurations is further characterized in that ink emitted from the above-mentioned head is cation cure ink.
According to the invention having the eighth configuration, cation cure ink has a higher sensitivity to active ray than radical cure ink, and is susceptible to active ray. However, a shielding member is provided between the head and active ray source. This arrangement prevents such cation ink from being thickened or cured, in the head or during the flight in air. Further, since the cation cure ink is used, ultraviolet light source with low illumination can be used as the active ray source to make it possible to provide a small sized and low-cost inkjet printer, which forms a stable and high image quality for a long period.